<!DOCTYPE html>
<html>
<head>
    <meta charset="utf-8" />
    <title></title>
    <style type="text/css">
        #p1{text-align:left;}
        #p2{text-align: center;}
        #p3{text-align: right;} 
    </style>
</head>
<body>
    <P id="P1"><strong>左对齐</strong>：好好学习，天天向上。</p>
    <P id="p2"><strong>居中对齐</strong>：好好学习，天天向上。</p>
    <P id="p3"><strong>右对齐</strong>：好好学习，天天向上。</p>
</body>
</html>